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CVE-2026-100769: Use-after-free in the JavaScript: WebAssembly component

• Severity: high (CVSS 8.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-29 · updated 2026-10-06
• Weakness: CWE-416

Description

Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, and Firefox ESR 140.17.

Affected products

• Mozilla Firefox: from 140.0.0 before 140.17.0; from 153.0.0 before 153.4.0; from 154.0.0 before 157.0.0 — fixed in 140.17.0, 153.4.0, 157.0.0
• Mozilla Thunderbird: from 140.0 before 140.17.0; from 153.0 before 153.4.0; from 154.0 before 157.0 — fixed in 140.17.0, 153.4.0, 157.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 140.17.0, 153.4.0, 157.0.0; Mozilla Thunderbird 140.17.0, 153.4.0, 157.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2067190
• https://www.mozilla.org/security/advisories/mfsa2026-100/
• https://www.mozilla.org/security/advisories/mfsa2026-101/
• https://www.mozilla.org/security/advisories/mfsa2026-102/
• https://www.mozilla.org/security/advisories/mfsa2026-103/
• https://www.mozilla.org/security/advisories/mfsa2026-97/
• https://www.mozilla.org/security/advisories/mfsa2026-99/

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